# How do I calculate a pumps psi output?

by jimhebert
Tags: output, pumps
 P: 29 I have a pump that puts out 396 gal/hr of water. The output pipe on the pump is 9/16 inch in diameter. Is there a way to calculate the psi?
 Mentor P: 22,282 It can be done but it isn't easy: you have to add up the pressure losses of all of the components of the piping system
 P: 29 Ok, I thought maybe there was a simple formula that could be applied. Thank You anyway. On second thought, the piping is the same size as the outlet and it is only about 6 feet long, but the pump will be pumping the water up. It's for an aquarium.
P: 1,472
How do I calculate a pumps psi output?

 Quote by jimhebert I have a pump that puts out 396 gal/hr of water. The output pipe on the pump is 9/16 inch in diameter. Is there a way to calculate the psi?
Pumps have a charcteristic that they will produce a certain flowrate at a certain head. I assume you mean 396 gal/hr at zero head. As the head is increased by adding more pipe to the pump exit, the flowrate decreases, up to a point where there will be a maximum pressure at the pump but no flow. By plotting several points on a graph of flow versus head, one obtains a pump characteristic curve.

The system curveon the other hand of all the losses in the pipe is more difficult to obtain as Russ mentioned.

The intersection of the system curve with the pump characteristic curve will give you the point at which the pump is operating.

 On second thought, the piping is the same size as the outlet and it is only about 6 feet long, but the pump will be pumping the water up. It's for an aquarium.
The 6 foot pipe section upwards will give only the elevation head loss for the system curve.
 P: 29 The 396 gall/hr is the flow rate with the 6 feet of head according to the chart that you are mentioning. So I guess it is still not possible to calculate the psi?
 P: 409 We can roughly approximate the head if we know the pump input power and the efficiency. The efficiency of pumps are usually between 60% and 70% and of the driver ( motor) is above 90%. The output power of the the pump is the flow rate times head. If the driver is running with for example 50 W, for the flow rate of 396 gal/hr ( about 0.0004 m3/sec), we will get $\Delta P=\frac{50\times 0.65 \times 0.9}{0.0004}=0.7 KPa$ which is about 7 meters of water .
 P: 29 These specs may help in your calculations. The pump is a 3.5 horsepower. The watts are 68, voltage =120, amps=.7 The Q max GPH = 687 gph The Q min GPH = 449 gph Head max =12.5 feet
P: 409
 Quote by jimhebert These specs may help in your calculations. The pump is a 3.5 horsepower. The watts are 68, voltage =120, amps=.7 The Q max GPH = 687 gph The Q min GPH = 449 gph Head max =12.5 feet
The pump horsepower seems too much! According to your number, your pump can do more work as 3 horses can do. Such a pump needs a powerful driver not a 68 watt one.
 P: 29 You mean it is not a 3.5 HP pump as the specifications say? According to your calculations, you believe it to be a 3 HP....Correct?
P: 409
 Quote by jimhebert You mean it is not a 3.5 HP pump as the specifications say? According to your calculations, you believe it to be a 3 HP....Correct?
I expected a much less hp. Something like 0.1 HP. Or perhaps its 3/5 hp rather than 3.5 hp.

See this online calculator http://www.engineeringtoolbox.com/pu...wer-d_505.html
 P: 29 In the calculator I entered q=687, and h=12.15 and shaft bph =3.52
P: 409
 Quote by jimhebert In the calculator I entered q=687, and h=12.15 and shaft bph =3.52

The calculator gets the flow in units of gallon/minute. Yours is per gallon/hour
 P: 29 I didn't notice that. This is a web page that says 3.5 HP and I also have the actual pump. http://www.petsuppliesnow.com/produc...UMP-660GP.html I'll call the company to find out what is going on.
 Sci Advisor PF Gold P: 3,636 That's a picture of an aquarium pump not a lawn sprinkler pump. That much power would wreck an aquarium. HP must mean something else. Probably "High Performance". Figure the power it takes to lift the weight of 687 gallons of water twelve and a half feet in an hour. F X D / T . (8.3 X 687) X 12.5 / 3600 = 19.8 ft-lbs/sec = .036 hp by my back of envelope, ~26 watts. To OP's question about discharge pressure - it's given in your spec. Centrifugal Pump "head" is the discharge pressure given in units " height of fluid flowing." Convert 12.5 feet of water to PSI. Were the pump instead pumping mercury, its discharge would be 12.5 feet of mercury and input power would be much higher.
 Sci Advisor PF Gold P: 3,636 Found its discharge curve.. http://www.f3images.com/IMD/MD_image...cra_Silent.jpg i'd say 3.5 meters is about all the useful lift you'll get. Credit is due this online store for posting the information. I like an outfit with that attention to detail. http://www.marinedepot.com/ps_viewit...content=XJ1141
 P: 29 I bought this pump in pet shop and they had one in use in an aquarium. I do want to use it in a large tank. I would still like to know the approximate PSI output curve if possible. The posted curve is not plotted correctly. The column with all the Syncras needs to be lifted up 2 increments and the H/m shifted to the right.
P: 409
 Quote by jimhebert I bought this pump in pet shop and they had one in use in an aquarium. I do want to use it in a large tank. I would still like to know the approximate PSI output curve if possible. The posted curve is not plotted correctly. The column with all the Syncras needs to be lifted up 2 increments and the H/m shifted to the right.
The plot seems fine. The column of Syncras is there just tell you ,by color , that which curve is for which pump. It has nothing with the vertical axis.

3.5 meters is not enough for your purpose? by the way, isn't pressure in unit of meters/ft of water easier to understand? I wonder why you keep asking the psi.
 P: 29 I want to attach another device to the pump and it requires a certain psi to function properly.

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